TL;DR : My beer has an acetaminophen aftertaste, what could this be ?
I brewed an espresso oatmeal Stout 4 months ago. It had a hard time carbonating and has an acrid/bitter (burnt? too much dark malt?) aftertaste. It mellowed a bit with time. To me, this aftertaste now resembles acetaminophen (without the coating, just the white stuff, which is pretty bitter).